Containers for storing hydrocarbons or various chemicals or pipes for transporting these materials include, for example, bottles for chemicals, fuel tanks for automobiles or small size engines, fuel pipes, etc. Many of the metals or glasses conventionally used as raw materials of these members have been now replaced with a plastic material as an alternative material. The plastic material has advantages such as a light weight, no need of a rust-proof treatment, less breakage, and a high degree of freedom of shape as compared with metals or glasses.
In most of the above applications, a high-density polyethylene (hereinafter sometimes abbreviated as “HDPE”) is used. HDPE has excellent mechanical strength, molding processability, and economical efficiency. However, HDPE has a disadvantage that an article stored in a container is likely to permeate through the HDPE wall and to be scattered in the air. Consequently, there is an increasing demand for a technique of enhancing the barrier performance of containers formed of a polyolefin such as HDPE or the like.
For example, as a method of enhancing the fuel barrier performance of an HDPE container, there is known a method of producing a single-layer container from a mixed source material prepared by blending a polyolefin with a gas barrier resin containing a metaxylylene group-containing polyamide for imparting barrier performance to containers and a modified polyethylene for adhering the polyolefin and the gas barrier resin (for example, see PTL 1).
In PTL 1, a mixed resin is kneaded in a single-screw extruder, then fed to a die via an adaptor or the like, and thereafter extruded out through the die to form a container. On this occasion, temperature conditions and the like of the single-screw extruder, the die, the adaptor and others are suitably set, so that the gas barrier resin is dispersed in a form of layers in the container obtained by extrusion through the die.
According to the method of PTL 1, any equipment for producing conventional HDPE containers may be used almost directly as such and, in addition, due to layer-like dispersion of the gas barrier resin, barrier performance comparable to that of multi-layer structures can be imparted to the produced containers. Moreover, the resin material that constitutes the mill ends and the purge waste formed in producing the containers is the same as the resin material that constitutes the containers, and therefore can be reused as a recycled material for the material to constitute the containers.